# desolve_system_rk4 lisp debugger Anonymous I am attempting to solve a system of 3 differential equations. Whenever I set the initial condition of the third variable not equal to 0, I get a lisp debugger error message. I have posted the code and the error message below. I should note that it runs as long as the initial condition of the third variable is equal to 0.

a,b,c,t=var('a, b, c, t')

#Parameter Values
r_a=1.09
r_b=1.1
k=500
alpha_a=0.11
alpha_b=0.11
beta_a=0.2
beta_b=0.2
d=0.5

#Differential Equations
aprime=r_a*a*(1-((a+alpha_a*b)/k))-beta_a*c*a
bprime=r_b*b*(1-((b+alpha_b*a)/k))-beta_b*c*b
cprime=beta_b*c*b+beta_a*c*a*-d*c

#Variables
variables=[a,b,c]

#Initial Conditions (t0,a0,b0,c0)
ic=[0,200,200,50]

#tfinal
tfinal=100

P=desolve_system_rk4([aprime,bprime,cprime],variables,ics=ic,ivar=t,end_points=tfinal)

Adata=[ [i,j] for i,j,k,l in P]

Bdata=[ [i,k] for i,j,k,l in P]
Bplot=list_plot(Bdata,color='blue')

Cdata=[ [i,l] for i,j,k,l in P]
Cplot=list_plot(Cdata,color='purple')

Aplot+Bplot+Cplot


To enable the Lisp debugger set debugger-hook to nil.

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I've not gotten this error before. But, I do recommend using one of the other ode solvers in Sage. You can see two examples that I've posted as responses here:

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